It is often extremely difficult to remove a screw-on cap from a container, such as a jar or bottle, and this is particularly true when a negative pressure is present in the container. The difficulties experienced by persons with no physical impairments in the manual removal of screw-on caps from containers are often magnified to insurmountable levels for persons who are physically impaired.
For many years, attempts have been made to develop devices to remove the screw-on caps from containers. U.S. Pat. No. 2,761,337 to Daniel discloses a manually operable gripper cone which assists the user in the manual removal of a container cap, and the development of these manual devices ultimately led to the design of motor driven bottle closure openers. U.S. Pat. Nos. 4,762,029 and 4,919,014 to Chen both disclose bottle closure openers which are motor driven and which include an angled cap engaging member to remove a cap from a bottle. In these units, a platform supporting the bottle moves the bottle upwardly into engagement with a rotating cap engaging member.
Similarly, U.S. Pat. No. 4,171,650 to Cardinal illustrates a jar lid loosening device wherein a jar supporting base moves a jar upwardly into contact with a cap removing clamping unit which is driven by a separate motor to remove the cap.
In the previously known motor driven container cap removers, it has been necessary to raise a stationary container into engagement With a rotating cap remover, an operation which often requires the use of multiple motors and a complex drive system. Often it is difficult to accurately control the upward movement of a container so as to maintain sufficient pressure between the container cap and the rotating removal device for cap removal while preventing the application of excessive pressure which will break or damage the container. As the cap is unscrewed, it moves longitudinally away from the container, and if effective compensation for this longitudinal movement is not provided, the increase of pressure on the container can result in damage to either or both the container and cap.
Finally, in known motor driven units where a stationary container is raised into contact with a rotating cap removal device, there is a tendency for the initial contact to cause the container to slip and rotate relative to its supporting base until sufficient pressure is applied longitudinally of the container to preclude this slipping movement. This pressure can be in excess of that which would be required to remove the cap if container slippage relative to the supporting base did not occur, and the presence of this higher pressure increases the likelihood that the container or cap will be damaged.